Conventionally, a vehicle brake device is known which is, for example, equipped with a master cylinder, an output piston which varies the volume of a master chamber by being driven by a force corresponding to a hydraulic pressure in a servo chamber, an input piston defining a first hydraulic pressure chamber filled with a brake fluid with the output piston and being movable in association with an operation of a brake operating member, a mechanical type servo pressure generating portion outputting a hydraulic pressure corresponding to the hydraulic pressure inputted in a pilot chamber into the servo chamber and a pilot pressure generating portion generating the hydraulic pressure corresponding to an inputted control signal in the pilot chamber. The vehicle brake device as described above is disclosed in a Japanese Patent Publication 2011-240873 A.
Further, as the mechanical type servo pressure generating portion, a mechanical type regulator for generating a hydraulic pressure corresponding to a pilot pressure in the servo chamber based on an accumulator pressure in an accumulator is disclosed in another Japanese Patent Publication 2013-193619 A.
As explained above, there exists a vehicle brake device which is equipped with a pressure adjusting device which outputs a servo pressure corresponding to the pilot pressure which is inputted to the pilot chamber to the servo chamber. Basically, the pressure adjusting device includes a piston which is driven by a force generated by a difference between the force corresponding to the pilot pressure and the force corresponding to the servo pressure and the volume of the pilot chamber is variable in response to the displacement of the piston. The servo pressure is one of the output pressures outputted in response to the pilot pressure.